HR: 14:40h
AN: G13C-05    [Abstracts]
TI: GPS-Constrained Microplate Kinematics and Plio-Pleistocene Tectonic Evolution of the North Anatolian Fault and North Aegean Sea
AU: * Thatcher, W
EM: thatcher@usgs.gov
AF: U. S. Geological Survey, MS/977 345 Middlefield Road, Menlo Park, CA 94025 United States
AB: Emerging evidence from Global Position System (GPS) survey measurements in the Aegean and elsewhere suggests that present-day active continental deformation occurs largely due to the relative motions of a small number of rigid blocks or microplates. However, it is not universally agreed whether the continental microplate description of the GPS data is superior to other proposed models, nor is it clear whether present-day movement patterns can be usefully extrapolated into the geologic past. Here I examine the known deformation history of the North Aegean over the past ~10 Ma and compare it with predictions based on the present-day microplate model. Agreement provides independent support for the GPS-based model and demonstrates its value in bettering our understanding of Aegean tectonics. If we knew nothing about late Cenozoic North Aegean tectonics and provisionally assumed the correctness of the Aegean microplate model of Nyst & Thatcher [2004 JGR], we would predict several features of the tectonic evolution that accord with geologic evidence. First, the North Aegean Sea would be created by extension due to SSW motion of the South Aegean and concomitant CW rotation of central Greece during the past 10 Ma. The same kinematic process would cause extension to be succeeded by strike-slip motion as the `ridge-transform-ridge' triple junction migrates WSW 24 km/Ma and the North Anatolian fault propagates into the region. The Plio-Pleistocene history of the North Aegean shows these same general features. Drilling and seismic imaging document the existence of young (< 10 Ma) and thick (up to 6 km) sedimentary sequences attributed to crustal extension by a factor of 3-4. Seismic profiling and bathymetric mapping show a mesh of roughly orthogonal faults with dip-slip offsets. Structural studies of sub-aerial exposures of these faults suggest an earlier episode of extension was followed by predominantly strike-slip motions. The plate kinematic reconstruction of late Cenozoic tectonics thus has several strengths but some clear limitations. Using only the GPS constrained microplate model and no adjusted parameters, backwards extrapolation over the past 10 Ma explains the observed large scale Plio-Pleistocene extension of the North Aegean and its evolution towards present-day strike-slip tectonics via the much-discussed propagation of the North Anatolian fault into the North Aegean. The spatial distribution of Plio-Pleistocene sediments and large-offset normal faults is considerably more complex than the simple extensional faulting pattern expected from the plate kinematic extrapolation. The detailed pattern of Plio-Pleistocene extension is compatible with several abrupt jumps in the principal zone of extension from NE to SW with time, which would account for the localized sediment accumulations in the Kavala and Thermaikos basins and the smaller than expected offset of the North Anatolian fault in the Dardanelles. The relative youth of extension in the Gulf of Corinth indicates the current geometry and motion of the Central Greece microplate is correspondingly recent, so the extrapolated rotation of this block during the past 10 Ma cannot be correct. Extension prior to about 1 Ma BP must have occurred elsewhere, perhaps in the central and southern Aegean.
DE: 8109 Continental tectonics--extensional (0905)
DE: 8110 Continental tectonics--general (0905)
DE: 8157 Plate motions--past (3040)
DE: 1206 Crustal movements--interplate (8155)
DE: 1208 Crustal movements--intraplate (8110)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting